Genetics
Dec 28, 2015
Genetics
11.1 – Gregor Mendel
Heredity
Inheritance of traitsGenetics - study of heredity
Genetics
Gregor Mendel
Suggested that paired factors, or genes, carry inherited traits.
Predicted how traits were inherited by studying pea plants
The Role of Fertilization
Fertilization - During sexual reproduction, male and female reproductive cells join to produce a new cell.
The Role of Fertilization
The Role of Fertilization
• Mendel had several true-breeding plants
• Self-pollinating and produce offspring identical to parent
• Trait - a specific characteristic of an individual
• Ex) Seed color and shape.
• Varies
The Role of Fertilization
• Mendel studied traits of pea plants.• Hybrids - Offspring between parents with
different traits.
Quick Graded Review – Two Options – 5 minutes
1. Stand and speak Summarize the notes in 15 seconds. Spend the next 3 minutes preparing what
you’ll say. 2. Schoology discussion
Go to Schoology your class Unit 7 11.1 Summary – First Half
Write a summary of the notes so far in at least 3 sentences.
Do not respond to anyone yet.
Genes and Alleles P gen – Parents - Original pair of plants
• F1 - Offspring of P generation.
• In each cross, the nature of the other parent, with regard to each trait, seemed to have disappeared.
Genes and Alleles
• Mendel’s first conclusion -
• An individual’s characteristics are determined by factors that are passed from one parental generation to the next.
• Genes - Factors that are passed from parent to offspring.
Dominant and Recessive Traits
• Mendel’s second conclusion• Principle of Dominance –
Some alleles are dominant, others are recessive.• If an organism has at least
one dominant allele for a trait,it will exhibit the dominant trait.
• If an organism has a recessive allele for a trait, it will exhibit the recessive trait only when there are no dominant alleles present.
Alleles
Different forms of a geneOrganisms have two alleles,
or genes, for each trait.One allele from the
female gamete (egg). One allele from the
male gamete (sperm).
Segregation
• What happened to the recessive alleles?
• Mendel allowed F1 hybrids to self-pollinate. The offspring of an F1 cross are called the F2 generation.
The F1 Cross
• When Mendel saw the F2 plants, he observed the recessive traits reappeared.
• About ¼ of the F2 plants showed the recessive trait.
Explaining the F1 Cross
• Alleles had segregated.
• Mendel suggested the alleles for tallness and shortness in the F1 plants segregated from each other during formation of the sex cells, or gametes.
Recessive trait
Dominant trait
Seed shape
Seed color
Flower color
Flower position
Pod color
Pod shape
Plant height
round yellow purpleaxial (side) green inflated tall
wrinkled green whiteterminal
(tips) yellow constricted short
Quick Graded Review – Two Options – 5 minutes 1. Stand and speak
Summarize this part of notes in 15 seconds. Spend the next 3 minutes preparing what you’ll say.
2. Schoology discussion Go to Schoology your class Unit 7
11.1 Summary – Second Half Write a summary of this part of notes in at least 3
sentences. Or respond and add on to someone else’s response
from First Half with information from notes.
Tongue Roll Dominant trait
Recessive attached ear lobesDominant Free Ear Lobes
Hitch hiker’s thumb
Dominant
Regular thumb
Recessive
Other examples
Chin cleft – Dominant Bent pinky finger – Dominant Dimples – Dominant Blue eyes – Recessive Hand clasp – Left thumb
dominant Widows peak - Dominant
11.2 – Applying Mendel’s Principles
Dominant gene (allele)
Stronger of two genes Represented by capital letter Written first Example: T for tall plant height
Recessive gene (allele)
Weaker of two genes Can be hidden by dominant genes. Represented with lower case letters Example: t for short plant height
Pure (Homozygous)
Two of the same genes (alleles) for a trait
Example: TT (homozygous dominant) or tt (homozygous recessive)
Hybrid (Heterozygous)
Two different alleles for a trait
Example: Tt Tall or short?
Probability
Probability – The likelihood that a particular event will occur.
Example: Flipping a coinProbability of flipping heads?
1
2
Number of total possible outcomes
Number of desired outcomes
Probability
Example: Flipping a coinProbability of flipping heads
three times?
½ x ½ x ½ = 1/8
Genotype
Combination of alleles or genes for a certain trait
Example: Tt, TT, tt
Phenotype
Physical, visible traits how it looks
Determined by looking at organism
Example: tall, short
Genotype or Phenotype?
TtRoundBlackBBSmoot
hrrTall
Genotype
Phenotype
Phenotype
Genotype
Phenotype
Genotype
Phenotype
In pea plants, green (G) pods are completely dominant over yellow (g).
What are the genotypes?
Homozygous yellowHeterozygous greenHomozygous dominantHybrid
ggGg
GG
Gg
In pea plants, green pods are completely dominant over yellow.
Pure yellow Homozygous recessivePure greenHeterozygous Yellow
gg
gg
ggGg
GG
In guinea pigs, short hair is dominant over long hair
What hair length will be represented by a capital S?
What hair length will be represented by a lower case s?
Short
Long
What phenotypes would result from the following genotypes?
SS ssSs
Short hair
Long hair
Short hair
T
T t
t
Tall plant
Short plant
All tall plants
What are the phenotypes of the parent plants?
If both parents are pure, what are their genotypes?
Which gene or allele can each parent pass on to the offspring?
What is the phenotype of the offspring?What is the genotype of the offspring?
TT t t
In pea plants, round pea pod texture is dominant over wrinkled texture. What is the genotype of the following?
homozygous roundheterozygouswrinkledpure dominanthybrid round
RR
Rr
rr
RR
Rr
In pea plants, round pea pod texture is dominant over wrinkled texture. What is the genotype of the following?
pure recessiveheterozygous roundpure wrinkledhybridpure round
rr
Rr
rr
Rr
RR
Punnett Squares
Punnett squares – used to predict and compare the genetic differences that will result from a cross.
Monohybrid crossesMonohybrid crosses
Heterozygous tall parent
T t
T t
T t
T
t
Heterozygous tall parent
TT Tt
Tt tt
How To Make a Punnett Square for a One-Factor Cross
Write the genotypes of the parents in a cross.
Ex) Cross a male and female bird that are heterozygous for large beaks. They each have genotypes of Bb.
Bb and Bb
How To Make a Punnett Square Draw a Punnett square. Put one parent on the top,
one parent on the left. Put one allele from each
parent on each side of each section.
How To Make a Punnett Square
Fill in the table by combining the gametes’ genotypes.
Mom
Dad
-Determine the genotypes and phenotypes of each offspring.
How To Make a Punnett Square
Probability of having…
A large beak? A small beak? Homozygous dominant? Heterozygous? Homozygous recessive?
3:4
1:4
1:4
2:4
1:4
Independent Assortment
Principle of independent assortment – genes for different traits can segregate independently during the formation of gametes.
Dihybrid Cross
Two factor crossTwo traits involved.
The Two-Factor Cross: F1
Mendel crossed two true-breeding plants:
One produced only round yellow peas
One produced onlywrinkled green peas.
The Two-Factor Cross: F1
The round yellow peas had the genotype RRYY, which is homozygous dominant.
The Two-Factor Cross: F1
The wrinkled green peas had the genotype rryy, which is homozygous recessive.
The Two-Factor Cross: F1
All F1 offspring were round yellow peas. Shows yellow and round alleles are dominant over the alleles for green and wrinkled.
Punnett square shows genotype of F1 offspring as RrYy, heterozygous for both seed shape and seed color.
The Two-Factor Cross: F2
Mendel then crossed the F1 plants to produce F2 offspring.
Crossed RrYy with RrYy
Dihybrid cross instructions
Cross the parent alleles.
Make sure each box has two of each letter, one from each parent
Mom
Dad
The Two-Factor Cross: F2
Alleles for shape segregated independently of those for color.
Genes that segregate independently do not influence each other’s inheritance.
The Two-Factor Cross: F2
Results were close to the 9:3:3:1 ratio the Punnett square predicts.
Mendel discovered the principle of independent assortment – genes for different traits segregate independently during gamete formation.
11.3 - Other Patterns of Inheritance
Incomplete dominance
Alleles BLEND (mix) Neither gene is dominantHeterozygous phenotype
is a blend of the dominant and recessive phenotypes.
Think about colors of paintRed + White = Pink
Codominance
Both alleles are dominantHeterozygous
expresses both phenotypes together.
There is NO “blending”Red + White = Red and White
Red cow crossed with white cow results in roan cattle. Roan cattle have both red and white hairs.
Codominance
Codominance
Example: White chicken
(WW) x black chicken (BB) = black and white checkered chicken (BW)
Codominance
Incomplete or Codominance?
A white cow and a red cow produce a roan cow, one that has both white and red hairs.
A red flower and a white flower produce pink flowers.
A black cat and a tan cat produce tabby cats, cats where black and tan fur is seen together.
Codominance
Incomplete
Codominance
Incomplete or Codominance?
A blue blahblah bird and a white blahblah bird produce offspring that are silver.
A certain species of mouse with black fur is crossed with a mouse with white fur and all of the offspring have grey fur.
A woman with blood type A and a man with blood type B have a child with blood type AB.
Incomplete
Incomplete
Codominance
Multiple AllelesSingle gene with
more than two alleles.
example: human blood type
Blood Types (codominant)
Blood type is codominant
IA and IB are dominant.
i is recessive4 different blood
types
Phenotype(Blood type)
Genotype(Alleles or genes for blood type)
A IAIA, IAi
B IBIB, IBi
AB IAIB
O ii
Polygenic Traits Traits controlled by two or more (many)
genes
Polygenic traits often show a wide range of phenotypes.
example: human skin color employs more than four different genes
Skin color genes: AaBbCcDd
Genes and the Environment The characteristics of any organism are
not determined solely by the genes that organism inherits.
Genes provide a plan for development, but how that plan unfolds also depends on the environment.
Both nature and nurture
14.1 – Human
Chromosomes
Karyotype
Chart of chromosome pairs arranged by decreasing size.
Shows unusual number of chromosomesCan detect trisomy 21 (Down syndrome)Identifies male or femaleShows genome – full set of
genetic information.
Karyotype
Normal Female
KaryotypeFemale with Down Syndrome
Sex Chromosomes
X and Y chromosomesDetermine the sex of the
offspringFemales are XXMales are XY
Sex Chromosomes
All other chromosomes are autosomes.
Everyone has 46 chromsomes:2 sex chromosomes and 44 autosomes.
Sex-linked Traits
Traits inherited on X and Y chromosomes.
Most are on the X chromosome (because it’s bigger)
Example) Color blindness is a recessive
sex-linked trait on the X-chromosomeMales show recessive
sex-linked traits more than femalesWhy?
Sex-linked Traits
Males get only one X chromosomeTherefore, males show all
recessive sex-linked traits on X chromosome.
Females have a second X chromosome that carries another allele that can hide recessive traits
Sex-linked Traits
Females who have recessive alleles but show the dominant trait (heterozygous) are called carriers
A woman can have normal vision but carry the recessive allele for colorblindness
X-Chromosome Inactivation If just one X chromosome is enough for
male cells, how does the cell “adjust” to the extra X chromosome in female cells?
In female cells, one X chromosome is randomly switched off, forming a Barr body.
Barr bodies are generally not found in males because their single X chromosome is still active.
Pedigree Study
Method of determining the genotype of individuals by looking at inheritance patterns
Pedigrees illustrate
inheritance
Pedigrees illustrate
inheritance
Male
Female
Affected male
Affected female
Mating
Parents
Siblings
Known heterozygotes for recessive allele
Death
Human Pedigrees This diagram shows what the symbols
in a pedigree represent.
Human Pedigrees This pedigree shows how one human trait
—a white lock of hair just above the forehead—passes through three generations of a family.
The allele for the white forelock trait is dominant.
Human Pedigrees Top of the chart is grandfather with the white
forelock trait. Two of his three children
inherited the trait. Three grandchildren have the trait,
but two do not.
Human Pedigrees Because the white forelock trait is dominant,
all family members lacking this trait must have homozygous recessive alleles.
One of the grandfather’s children lacks the white forelock trait, so the grandfather must be heterozygous for this trait.